1. Field of the Invention
The present invention relates to a mold clamping apparatus of an injection molding machine and to a method of adjusting effective lengths of tie bars.
2. Description of the Related Art
A mold clamping apparatus shown in FIG. 6 has been known as a mold clamping apparatus provided to an injection molding machine. FIG. 6 is a view schematically showing a related molding clamping apparatus, in which FIG. 6A is a front view thereof, and FIG. 6B is a sectional view taken along a line XI-XI of FIG. 6A.
The mold clamping apparatus 101 shown in FIG. 6 includes a fixed platen 106 to which a fixed-side mold 106a is attached, a movable platen 107 to which a moving-side mold 107a is attached and which is capable of moving with respect to the fixed platen 106, and a mold clamping housing 108 which is connected to the movable platen 107 through a toggle link type or direct hydraulic pressing mechanism 111. Four tie bars 102A to 102D are provided between the fixed platen 106 and the mold clamping housing 108, and the movable platen 107 can move along the tie bars. Male screws are formed at both end portions of each of the tie bars 102A to 102D, tie bar nuts 110 are screwed to the male screws at the side of the fixed platen 106, and female screws formed in mold thickness adjusting units 109 are screwed to the male screws at the side of the mold clamping housing 108. The effective length of each of the tie bars can be adjusted by varying the distance between the tie bar nuts 110 and the mold thickness adjusting units 109.
As the method of changing the effective lengths of the tie bars, a first method of varying the distance between the tie bar nuts 110 and the mold thickness adjusting units 109 by providing die height adjusting nuts to the mold thickness adjusting units 109 and by rotating the die height adjusting nuts has been known. Further, a second method of varying the distance between the tie bar nuts 110 and the mold thickness adjusting units 109 by forming the male screws formed at both end portions of each of the tie bars as screws inversed to each other or by forming pitches thereof different to each other, and by rotating only the tie bars in a state in which the tie bar nuts 110 and the mold thickness adjusting units 109 are fixed has been known. The first method is disclosed in Japanese Patent No. 3549280.
The balance of the extended amount of the four tie bars 102A to 102D when the mold clamping force is generated by operating the mold clamping apparatus 101, and furthermore the balance of the mold clamping force acting on the molds can be adjusted by adjusting individually the effective length of each of the tie bars by the above-described methods.
However, the first method has following problems.
(1) The operation of the injection molding machine needs to be stopped to adjust the effective lengths of the tie bars, and molded products cannot be manufactured during the adjustment.
(2) Since a unit (such as servomotor) for driving each of the die height adjusting nuts is separately required, cost of manufacturing the mold clamping apparatus increases remarkably, whereby it is not practical.
(3) Since the adjustment is rarely completed by performing the adjusting operation only one time, and it is needed to repeat many times the operation and the stoppage of the injection molding apparatus until the adjusting operation is completed, the adjusting operation takes labor and long time.
(4) Since the product molded through a test during the adjustment cannot be shipped as a product and should be discarded, as the adjusting operation is repeated in many times, the amount of wasted material increases.
Furthermore, the second method has following problems.
(1) The operation of the injection molding machine needs to be stopped to adjust the effective lengths of the tie bars, and molded products cannot be manufactured during the adjustment.
(2) Although the tie bar is fixed by any fixing means so that it is not rotated during the normal operation, it is necessary to disassemble the fixing means and to release the fixation during the time of performing the adjusting operation.
(3) The adjustment is rarely completed by performing the adjusting operation only one time, and it is necessary to repeat many times the operation and the stoppage of the injection molding apparatus, and the disassembly and the assembly of the fixing means until the adjusting operation is completed. Therefore, the adjusting operation takes labor and long time.
(4) Since the product molded through a test during the adjustment cannot be shipped as a product and should be discarded, as the adjusting operation is repeated in many times, the amount of wasted material increases.